Coated abrasive articles are used to abrade a wide variety of substrates or workpieces, such as, for example, wood, wood-like materials, plastics, fiberglass, soft metal alloys, enameled surfaces, and painted surfaces. One problem common to all of these different substrates or workpieces is "loading" or clogging, i.e., particles from the workpiece undergoing abrasion become lodged between the abrasive grains, thereby reducing the cutting ability of the coated abrasive, even though the abrasive grains are not worn. Consequently, loading substantially reduces the useful life of a coated abrasive article. In an attempt to overcome this problem, U.S. Pat. Nos. 2,768,886; 2,893,854; and 3,619,150 disclose the use of a coating comprising a metal stearate, metal palmitate, or metal laurate applied over the layer of abrasive grain. These patents disclose that the metal can be selected from the group consisting of magnesium, calcium, strontium, barium, chromium, zinc, cadmium, aluminum, and lead.
Coated abrasive articles are typically converted into a wide variety of different forms such as discs, cones, and sheets. If the converted form is a disc, it is often preferable to have a layer of pressure-sensitive adhesive coated on the major surface of the coated abrasive disc not bearing the abrasive grains. The coated abrasive disc can then be secured to a support pad and when the abrasive disc is consumed, it can be removed and replaced with a new abrasive disc. Such coated abrasive discs are typically packaged in roll form, with the result that the pressure-sensitive adhesive from one disc comes in contact with the grain-bearing surface of another disc. If the disc contains a metal stearate coating, e.g., zinc stearate, there is a tendency for the metal stearate to transfer from the grain-bearing surface of one disc to the pressure-sensitive adhesive surface of the other disc. If the metal stearate does transfer, it significantly reduces the adhesion characteristics of the pressure-sensitive adhesive. This can detract from operating performance. For example, if the adhesive strength of the pressure-sensitive adhesive is insufficient, the coated abrasive disc may not adhere properly to the support pad, and during use, the coated abrasive disc could fly off the pad, thereby forcing the operator to cease abrading operations.
One solution to the stearate transfer problem is to have a release liner containing a low surface energy material placed over the layer of pressure-sensitive adhesive. However, the use of a release liner poses additional problems for operators. A typical low surface energy coating of a release liner consists of silicone-based materials. When coated abrasive discs are utilized in paint related areas, the liner can come into contact with a painted surface, and the silicone can transfer to the painted surface and contaminate it. Also, operators must dispose of the liners and silicone-containing materials, which results in increased cost. For these reasons, it is preferable that coated abrasive discs that utilize a layer of pressure-sensitive adhesive not have a liner associated with them.
It is thus desired to have coated abrasive discs that have both a loading resistant coating and a layer of pressure-sensitive adhesive without a liner, but in which the material of the loading resistant coating of one disc does not significantly transfer to the layer of pressure-sensitive adhesive of another disc.
U.S. Pat. No. 4,486,200 discloses lithium stearate as a lubricant for non-woven abrasive products and U.S. Pat. No. 4,784,671 discloses lithium stearate as a lubricant for grinding wheels. Japanese patent application Kokai No. 56-69074 pertains to a coated abrasive containing a fatty acid metallic soap that has been treated with a surfactant. The metal can be selected from the group consisting of calcium, zinc, lithium, and barium; and the fatty acid can be selected from the group consisting of stearic, palmitic, oleic, and lauric acids. None of the foregoing references teach the use of a coated abrasive containing both a lithium salt of a fatty acid as a loading resistant coating and a layer of pressure-sensitive adhesive.